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richa 25th July 2011 12:28 PM

sick amp please help
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hi everyone, new here , hope i'm in the right place. i'll start with my first problem....., not a hi fi amp but a chip amp all the same, i have an indie sky 10 guitar amp (please don't laugh, i know it's a bit rubbish , all the same it does suit my purposes very well at the moment, problem is it's given up the ghost.., guitarist friend used it on a jam session a while back and it was used very hard all day,,, it then just stopped. he gave it to me (if i could fix it!!!!) to use in my home studio. even though its not great the overdrive channel sounded ...goood.
this is the problem.
1. it doesn't power up, no pilot light, no switch on thump or anything
2. there is no evidence of blown components, no burning at all and no damage to any components
3.i have checked the transformer, there appears to be no voltage at all from the power transformer, or any voltage anywhere on the board. (it did say .03 volts (ac at the transformer)????,
could it simply be power supply problem?
brief rundown
the amp is rated at 10 watts output, it uses tda 2050A chip
the power diodes are 1n4002 ( 4 of)
the transformer siply gives 4TZ-10, TY0603, cant find any info on this at all,.... i assume it is split rail ( red black red on the output side, any idea on voltages ??? (for replacement)
Please help!!!! the photos give you an idea of layout.
i have built ("from kits") a pair of maplin 50 watt mono blocks with uprated power supplies,(individual to each channel,) and a pre amp, they are rather goood, these are kit amps and i merely followed the instructions but when it comes to troubleshooting i'm a bit lost. could anyone give any help on the indie repair, there is no point buying anything else as i'm sure it must be a simple repair, anyway thanks in advance for any help you can give,,

johnr66 25th July 2011 03:10 PM

Did you try the fuse?

1) Unplug the amp from the electrical supply, unplug the white chip amp wire, unplug the transformer secondary. Change the fuse. Plug in to power and turn on. (leave other stuff unplugged). Did fuse blow? If yes, then it has a bad transformer or short somewhere in the live wiring. Go to step two if fuse is good.

2) turn off power and plug secondary back into board. turn on. If fuse blows, check rectifier diodes and filter caps. Could be a short/bad component somewhere on the board. If fuse is still good, go to 3.

3) turn off power and plug in the white ribbon cable for the output IC. Turn on. If fuse blows, the IC is bad.

At 10 watts, the TDA2050 IC is well under driven and should be reliable, however, the marginal heatsink looks troubling. The ribbon cable connection back to the main board also is a troubling design as most of the components are quite a distance from the power IC. It should have had the IC on board or with a daughter card with the ICs external components on it.

richa 25th July 2011 03:17 PM

hi thanks for reply so quick, no fuse doesn't, hasn't blown, the amp does nothing??
yeah i thought the heatsink was a bit rubbish, if i can get it going i will replace it with a better one, i have loads of them in a box, it was working fine but as i say it was given some stick for a few hours and then nothing,

johnr66 25th July 2011 03:37 PM

Sounds like the transformer is shot or the power switch has broken. See if you get voltage to the primary.

richa 25th July 2011 03:46 PM

hi' yeah i suspected transformer from start, trouble is identifying the right one, any suggestions, is it split rail? maplin sell one that looks similar but i appreciate you can't stick any old thing in it, i intend to get it working ( it is now my quest lol) and uprate heatsink and put a dedicated pre-out socket on the back, and use my beast power amp (150 watts) should i use it outside (maybe,), im bass player but also play guitar and for what it is , i'd use this indie for guitar , could you recommend transformer replacement , might as well just replace it, it's not going to be too exprnsive, thanks for your help

Mooly 25th July 2011 04:50 PM

Unplug from mains and see if you can get a reading on the ohms range on your meter when connected across the transformer primary. That's between the white and black ??? wire (that looks mainly out of sight). It should read quite low ohms.

If it's open circuit then more than likely there is a thermal fuse (non replaceable) buried in the transformer windings. If that's failed then it's likely there is a short somewhere... the IC or the bridge rectifier.

Always power anything like this up with a bulb tester to prevent excess current in the event of a fault.

richa 25th July 2011 04:54 PM

hi, yeah keep coming back to transformer, which seens dead, no output at all, alll wiring checks out ok, trouble is identifying which replacement to get???, thanks for your help

Mooly 25th July 2011 05:03 PM

The TDA2050,

runs on nominally -/+22 volt rails or lower. That means most likely a 15-0-15 vac transformer which would give approximately that.

Something like this,

or even,

Those diodes look like IN4001's which are only 1 amp so that kind of defines what we are looking at capacity wise.

richa 26th July 2011 12:14 PM

thanks to you all for your help, one other question, if i replace the trans. how do i decide which is th =15, and -15 sides of the wiring ,on the board, don't want to fry anything on board, guess i've to decide if it actually is worth 15 or 20 quid to fix!!!!,

richa 26th July 2011 12:15 PM

the diodes are 1n 4002, does this mean another type of transformer??

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